A typical differential global positioning system (DGPS) network includes a receiver which receives ephemerides data from satellites. Typically, such data is received from global positioning system (GPS) satellites which are a part of the GPS satellite network or satellites which are a part of the Global Navigation Satellite System (GLONASS). The ephemerides data is processed via an electronics package located within the GPS unit. The GPS unit receives differential correction data through a separate radio which is typically connected to the GPS unit by cable. The differential correction data is typically obtained from a radio coupled to a GPS unit which is located at a fixed site which is placed at a known location or it is obtained from other sources and is conveyed via radio. By processing the differential correction data together with the data received at the particular GPS receiver, the location of the GPS unit may be determined within a high degree of accuracy. This same method may be used to perform real time kinematic (RTK) surveys so as to accurately determine the relative position of the GPS system with sub centimeter accuracy.
Prior art GPS devices used in DGPS applications and RTK applications typically require numerous separate, distinct component units which are connected via cables. For example, the GPS receiver and processor would constitute one unit and the terrestrial radio would constitute a second unit which would be coupled to the GPS processor via cable. Typically, an input/output (I/O) unit which includes a display for data monitoring and a keypad for data input is also required. The I/O unit is coupled to the GPS receiver/processor unit and to the terrestrial radio via cable. Some systems also require the attachment of a separate battery via cable. Because multiple separate units are used in these prior art systems, the systems are bulky and they are difficult to move around.
For example, one type of prior art system which is typically referred to as "handheld" includes a GPS antenna, a GPS processor, a display processor, and a display in a single unit. A DGPS radio antenna and receiver are provided in a separate unit or units which are connected to the GPS processor. Another type of prior art system places the GPS antenna in an antenna unit and the display in a separate display unit. The GPS processor and the display processor may be contained in the GPS antenna unit, the display unit, or in a separate unit. A DGPS radio antenna and receiver are provided in a separate unit or units connected to the GPS processor. This format allows the user to separate the GPS antenna and the display units so that the GPS position and time information can be observed and operated upon in a protected environment.
The use of multiple units to house the various components required for prior art DGPS systems, and the requirement for cables and connectors to couple the units creates problems regarding reliability and durability. This is particularly true for DGPS systems which are mobile and which are jarred and shaken by use and movement. In addition, the systems are expensive to manufacture and assemble. Furthermore, the connections are often bulky, expensive and prone to breakage or malfunction. In addition, it is difficult to move the various boxes and cables around.
Typically, the GPS unit receivers are separated by long distances or by immobile structures; therefore, radio relay units are used to get the signal from one GPS unit to anther GPS unit. Prior art radio relay systems for relaying GPS signals typically include multiple separate components such as a transceiver operating at one frequency which is coupled via cable to a separate transceiver operating at a second frequency. These relay systems typically receive signals through an antenna which is cabled to a processor which is then cabled to a radio which rebroadcasts the signal through an antenna attached by cable to the radio. These relay systems are bulky and difficult to move around. Furthermore, these relay systems typically are expensive and are difficult to maintain and operate due to the fact that each of the components of the radio relay system is unique. In addition, most of the currently available systems are not durable and reliable enough for applications such as RTK surveying and operation in harsh environments such as construction sites.
What is needed is a simple GPS network which is easy to move from place to place and which is durable, reliable, and inexpensive to manufacture and assemble. More specifically, a GPS network which includes a GPS unit, a radio and a radio relay which will reliably operate in difficult environments such as those presented by repeated movement and use in harsh environments such as construction sites is required. Also, a GPS network consisting of components which are easy to operate, use and maintain is required.